Method and apparatus for maintaining substantial uniformity in the temperature of a heat-exchanging fluid

ABSTRACT

A heat exchanger and method for operating the same according to which the temperature of a heat-exchanging fluid is maintained substantially uniform. The heat exchanger has two groups of tubes in which an inner heat-exchanging fluid flows while an outer heat-exchanging fluid flows across the exterior of these tubes. The groups of tubes form first and second groups with the outer fluid flowing first across the first group and then across the second group, to form an entering stream of outer fluid flowing across the first group and an exiting stream of outer fluid flowing across the second group of tubes. Each of these streams is composed of first and second stream portions which have predetermined relationships with respect to the heat exchanger axis, and through a suitable baffle structure the first portion of the entering stream is deflected to form the second portion of the exiting stream while the second portion of the entering stream is deflected to form the first portion of the exiting stream, so that in this way substantial uniformity is maintained in the temperature of the exiting stream.

United States Patent [191 Beckmann et a1.

[ METHOD AND APPARATUS FOR MAINTAINING SUBSTANTIAL UNIFORMITY IN THETEMPERATURE OF A HEAT-EXCHANGING FLUID [75] Inventors: Georg Beckmann;Paul Viktor Gilli,

both of Vienna; Josef Lippitsch, Graz, all of Austria [73] Assignee:Waagner- Biro Aktiengesellschaft, Vienna, Austria 22 Filed: Feb. 8, 197321 Appl. No.: 330,623

[30] Foreign Application Priority Data Feb. 9, 1972 Austria A 1027/72[52] US. Cl. 165/145, 161/163 [51] Int. Cl F28f 9/22 [58] Field ofSearch ..165/140,145,l,140,141, 165/163, 159

1 51 Feb.4,l975

Primary Examiner-Charles Sukalo Attorney, Agent, or Firm-Steinberg &Blake [57] ABSTRACT A heat exchanger and method for operating the sameaccording to which the temperature of a heatexchanging fluid ismaintained substantially uniform. The heat exchanger has two groups oftubes in which an inner heat-exchanging fluid flows while an outerheat-exchanging fluid flows across the exterior of these tubes. Thegroups of tubes form first and second groups with the outer fluidflowing first across the first group and then across the second group,to form an entering stream of outer fluid flowing across'the first groupand an exiting stream of outer fluid flowing across the second group oftubes. Each of these streams is composed of first and second streamportions which have predetermined relationships with respect to the heatexchanger axis, and through a suitable baffle structure the firstportion of the entering stream is deflected to form the second portionof the exiting stream while the second portion of the entering streamisdeflected to form the first portion of the exiti ng stream, so thatthis wail substantial uniformity is maintained in the temperature of theexiting stream.

12 Claims, 14 Drawing Figures PATENTEU FEB 4197s SHEET 1 [IF 3 METHODAND APPARATUS FOR MAINTAINING SUBSTANTIAL UNIFORMITY IN THE TEMPERATUREOF A HEAT-EXCHANGING FLUID BACKGROUND or THE lNVENTION The presentinvention relates to heat exchangers.

In particular, the present invention relates to heat exchangers in whichan inner heat-exchanging fluid flows along the interior of successivegroups of tubes while an outer heat-exchanging fluid flows across theexterior of these tubes, with the inner fluid flowing only once throughthe inner tubes. The heat exchangers of this type are particularlysuitable for nuclear power plants.

With heat exchangers of this type each group of tubes has a considerablevariation in the temperature of the inner fluid which flows within thetubes, so that'as a result the outer fluid forms a stream in which thetemper ature is not uniform. This-lackof uniformity in the temperatureof the outer stream of fluid is highly undesirable. ln order toalleviate this problem it has already been proposed to arrange the heatexchanger tubes in such a way that the tubes of one group cross eachother before forming the tubes of a second group, so that through thisexpedient the positions occupied by the tubes of the different groupsare reversed with respect to each other in order to attempt to achieve auniformity in the temperature of the heated outer fluid. However, thistype of construction is exceedingly complex because of the complex pathsalong which the tubes must extend. This type of construction requires avery large space and involves high costs in assembly of the components,in addition to resulting in an undesirably high pressure loss, so thatsuch arrangements have proved to be uneconomical particularly with heatexchangers which have but one pressure vessel. It is also known tosituate between two groups of tubes a throttling device or a plate whichis punched wtih openings passing therethrough, in order to alleviate theabove problem. This type of construction, however, has the greatdisadvantage of creating an undesirable loss of pressure in the outerfluid which flows across the exterior of the tubes without avoiding anundesirable formation of bodies ofthe outer fluid which do not mix witheach other. Thus, the outer marginal currents of the outer fluid and thecentral currents thereof do not mix with each other with these knownarrangements.

A further disadvantage encountered with conventional apparatus andmethodof the above type is that static or aperiodic instabilities areencountered, which is to say that with the heat exchanger tubes arrangedin parallel large differences in the cross section of fluid flow and intemperatures at different parts of the fluids occur at individual groupsof tubes, particularly because of the formation of bodies of the outerfluid which do not mix with the remainder of the outer fluid, and thesefactors create a hazardous operation which renders the operatingconditions unsafe.

SUMMARY OF THE INVENTION A It is accordingly a primary object of thepresent ining heat-exchanging fluid without resorting to complex tubularstructures.

Furthermore, it is an object of the present invention to provide a heatexchanger apparatus and a method of operation according to which it ispossible to achieve the desired uniformity in the temperature of thedischarging fluid without creating any substantial loss in pressureduring flow of the fluid through the heat exchanger.

Also it is an object of the present invention to provide a method andapparatus of the above type which can be used either with radial or withaxial heat exchangers.

' In addition it is an object of the present invention to provide amethod and apparatus of the above type which require only simpleinexpensive changes to be made in conventional heat exchangers.

In accordance with the method and apparatus of the present invention theheat exchanger is composed of at least two groups of tubes which have apredetermined relationship with respect to each other and the axis ofthe heat exchanger. An inner heat-exchanging fluid flows along theinterior of these tubes while an outer heat-exchanging fluid flowsacross the exterior of these tubes. The outer fluid which flows acrossthe exterior of the tubes includes an entering stream which contacts thefirst group of tubes and an exiting stream which contacts the secondgroup of tubes, this entering stream being composed of first and secondportions which have respectively predetermined relationships withrespect to the heat exchanger axis while the exiting stream is alsocomposed of first and second portions which have the same predeterminedrelationships with the heat exchanger axis as the first and secondportions of the entering stream, respectively. According to the methodand apparatus of the present invention the first and second portions ofthe entering stream are deflected before they reach the second group oftubes in such a way that the first portion of the entering stream formsthe second portion of the exiting stream and the second portion of theentering stream forms the first portion of the exiting stream, so thatthrough this interchange of the relationships between the streamportions the desired uniformity is achieved in an exceedingly simple yethighly effective manner.

Thus, the apparatus of the invention will include suitable bafflessituated between the groups of tubes for deflecting the stream of outerfluid to achieve the above results. These baffles may be arranged so asto divide the stream of outer fluid into a plurality of subsidiarystreams which are individually treated to achieve the above objects.Thus, where the two groups of tubes are arranged along a common axis ofthe heat exchanger within an outer shell which forms a means fordirecting theexterior gas across these tubes, the part of the gas whichis situated adjacent the axis at the first group of tubes is deflectedto flow along the shell at the second group of tubes while the part ofthe gas in the region of the shell at the first group of tubes isdeflected to flow along the axis near the center of the second group oftubes. The deflection of the gas currents may be through for the partialstreams and the baffles may have a helical configuration withoutproducing any substantial reduction in the cross section of flow of thegas streams so that there is no undesirable loss of pressure.

The method and apparatus of the present invention are of particularimportance in connection with heat 3 exchangers where the groups oftubes are inaccessible as is the case, for example, with nuclear steamgenerators or heat exchangers. Where there are no intermediate headers,as is the case with steam boilers through which the fluid flows onlyonce, the equallizing mixing effect resulting from the use ofintermediate headers, injection coolers, or the like, to contribute tothe uniformity of the temperature of the outer fluid is no longeravailable. Since it is possible that some of the tubes will becomedamaged, the heat exchanger structure should have the capability ofplacing the damaged tubes out of operation without creating undesirableinstability in the current flow, and particularly with respect to thislatter problem the method and apparatus of the present invention are ofspecial importance because any lack of uniformity in the temperature ofthe discharging gas which otherwise would occur by taking damaged tubesout of operation are eliminated with the method and apparatus of thepresent invention.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way ofexample in the accompanying drawings which form part of this applicationand in which:

FIG. I is a schematic elevation view of a heat exchanger according tothe invention illustrating the manner in which fluid flows;

FIGS. 2-4 are respectively schematic sectional plan views taken alonglines Il-II, III-Ill, and Iv-IV of FIG. I and illustrating in additionthe direction of fluid flow;

FIGS. 5 and 6 are respectively schematic sectional plan viewsillustrating further possible embodiments of the method and apparatus ofthe invention at a location between two groups of tubes;

FIG. 7 is a schematic sectional elevation of another embodiment of themethod and apparatus of the invention at the location between two groupsof tubes;

FIG. 8 is a schematic plan view of the structure of FIG. 7 as seen whenlooking down on the structure of FIG. 7 in the direction of the arrowVIII of FIG. 7;

FIGS. 9 and 10 are respectively sectional plan views of the structure ofFIG. 7 taken along lines IX-IX and X-X of FIG. 7 in the direction of thearrows;

FIG. 11 is a schematic sectional plan view of the structure between thetwo groups of tubes, showing yet another embodiment where this structureis cylindrical rather than rectangular as shown in FIG. 8;

FIG. 12 is a sectional elevation of a radial heat exchanger, ascontrasted with the axial heat exchanger of the above embodiments, whichincludes the method and apparatus of the present invention;

FIG. 13 is a schematic sectional elevation of yet another embodiment ofthe invention according to which the tubes are twisted in apredetermined manner; and

FIG. 14 is a schematic fragmentary sectional elevation of a furtherembodiment of a heat exchanger method and apparatus according to theinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. I, there isschematically illustrated therein an axial heat exchanger having a loweror first group of tubes 2 arranged around the vertical heat exchangeraxis which coincides with the axis of a central vertical tube coaxiallysurrounded by the outer shell 17 of the heat exchanger.

The lower or first group of tubes 2 is followed by an upper or secondgroup of tubes 3 spaced axially from the lower group of tubes 2 and alsosituated within the shell 17. This shell 17 forms a means for directingan outer fluid in the form of a gas upwardly across the first group oftubes 2 and then across the second groups of tubes 3. In this way thestream of outer fluid forms an entering stream 31 and an exiting stream32.

In addition it will be noted that the lower group of tubes 2 is dividedby a cylindrical partition into an inner subgroup of tubes II and anouter subgroup of tubes 12 while the upper group of tubes 3 iscorrespondingly divided by a cylindrical partition into an innersubgroup of tubes 13 and an outer subgroup of tubes 14. Thus, at eachgroup the subgroups are concentric.

As a result of this arrangement the entering stream 31 is divided intoinner and outer stream portions which respectively flow across thesubgroups I1 and 12, while the exiting stream 32 is also divided intoinner and outer stream portions which respectively flow across thesubgroups l3 and 14.

In accordance with the invention, in the space 1 be tween the firstgroup of tubes 2 and the second group of tubes 3 there is a bafflemeans, which includes the plates 4, serving to deflect the streamportion which flows across the inner subgroup 11 so that it will flowacross the subgroup 14 while also deflecting the stream portion whichflows across the subgroup 12 so that it will flow across the subgroup13. In this way the parts of the entering stream 31 which have aparticular relationship with respect to each other and with respect tothe axis of the heat exchanger become interchanged with those parts ofthe exiting stream 32 which have the same relationship with respect toeach other and with respect to the axis of the heat exchanger. In orderto illustrate this action clearly, the stream portion flowing across thesubgroup 12 is designated by a solid arrow 15 while the stream portionflowing across the subgroup 11 is designated by a dotted arrow 16. Itwill be noted that in the space 1 because of the baffle means, thesearrows cross each other with the stream portions being deflectedsubstantially radially with respect to the heat exchanger axis insubstantially opposite directions, so that at the second group of tubes3 the arrow 15 is situated at the inner subgroup I3 and the dotted arrow16 is situated at the outer subgroup 14.

It will be noted that in addition to the above features the directionsof winding of the subgroups l1 and 12 are opposite to each other toprovide the opposed circular directions of flow indicated respectivelyby the arrows l5 and 16. Moreover, with the heat exchanger acountercurrent heat exchange is preferred according to which the innerfluid in the interior of the tubes flows downwardly while the exteriorfluid flows upwardly as shown in FIG. 1. Of course, the two groups oftubes 2 and 3 communicate with each other. In order to facilitateunderstanding of the invention and clarity of illustration the detailsof the tubes and their connections are not shown. FIGS. 2 and 4respectively illustrate also how the gas stream portions haveinterchanged their relative positions while maintaining theirpredetermined relationship with respect to the heat exchanger axis.

As may be seen from FIG. 3, the plates 4 of the baffle means are flatplates situated respectively in planes which contain the axis of theheat exchanger, these plates being uniformly distributed about the axisin such a way that each partial gas stream is deflected throughapproximately 180.

FIG. 5 shows how it is possible to arrange the plates 4 in such a waythat they define two groups of spaces which alternate with each other,with one group of these spaces accommodating the tubes whichinterconnect the groups 2 and 3 while the remaining spaces accommodatethe baffle means which includes, in addition to the plates 4, the plateswhich are described in greater detail below. Thus it will be seen fromFIG. 5 that intermediate tube portions 5 extend through the illustratedspaces defined between the plates 4 in order to maintain the tube groups2 and 3 in communication with each other. These tubes 5 also act assupports. The baffles 10 are in the form of suitably twisted or curvedplates shown for the sake of simplicity and clarity in only one of thespaces between a pair of successive plates 4. The configuration of theplates is such that the deflection of each partial gas stream through180 will be achieved. Thus, with thisdeflection those parts of thestream which are close to the axis become situated close to the shell l7while those parts which are initially close to the shell 17 becomelocated close to the axis.

According to the embodiment of FIG. 6, instead of utilizing flat plates4, the'one group of spaces, which alternate with the other group inwhich the tubes 5 are accommodated, are defined by cylindrical plates 4spaced as illustrated in FIG. 6 to define between themselves biconcavespaces for accommodating the tubes 5. Within each cylindrical wall 4there are the baffles 10 as described above to provide the deflectionthrough 180 as pointed out above.

FIGS. 7-10 illustrate another embodiment according to which the heatexchanger section between the two groups of tubes is of a rectangularsection with the baffle means 6, 7 taking the form of oppositely curvedplates of helical configuration providing helical surfaces for guidingthe partial gas streams.

As may be seen from FIG. 8, which is a top plan view of the structureshown in FIG. 7, the baffles define flow channels of pentagonalconfiguration, as illustrated by the heavy lines in FIG. 8, with thebaffles or walls 6 and 7 providinghelical surfaces to guide the gas sothat pentagonal entrance channels illustrated by the heavy lines aretransformed into pentagonal exit channels as shown by the thin lines.One of the entrance areas includes the corners -24 while the corners ofan exit area are indicated by the reference characters -29. The channelwalls 8 and9 are plates formed by a section through the helical baffles6 and 7. If desired these walls 8 and 9 can be eliminated withoutdetracting from the desired operation of the baffle means which wouldthen consist only of oppositely directed helical surfaces. In the planview of FIG. 8 the heavy lines are at the front while the thin lines areat the back. The guide surfaces of the baffles are skewed backwardly anddefine an edge, these surfaces being hatched at the horizontal sectionline.

FIG. 9 is the section midway between the top and bottom of the structureof FIG. 7 while FIG. 10 shows the arrangement adjacent the bottom of thestructure of FIG. 7.

As is apparent from the above description and the illustration of FIGS.7-10, the baffle means does not create any appreciable reduction in thecross section of flow of the gas streams from the first group of tubes 2to the second group of tubes 3, so thatas a result no undesirable lossof pressure is created during deflection of the gas currents.

In FIG. 11 there is a plan view of another embodiment which iscylindrical, rather than rectangular as shown in FIG. 8. In this casealso the entrance and exit channels are illustrated with the upper edgesshown in thick lines and the lower edges shown in thin lines. Thedesignation of the helical surfaces has been carried out in FIG. 11according to the same scheme as in FIG. 8 but in only two adjacentchannels for the sake of clarity. Thus, in this case also the bafflesare in the form of helical deflector plates arranged in groups 18, 19with partition plates being provided to define spaces through which theconnecting tube portions 5 can extend.

FIG. 12 shows how the invention can be applied to a radial heatexchanger. Thus as schematically illustrated in FIG. 12, the enteringstream 31 is deflected by a conventional baffle of inverted conicalconfiguration so that the entering stream now flows radially away fromthe vertical axis of the heat exchanger which coincides with the axis ofthe inverted conical baffle 40. Thus, the entering stream will firstflow across the first group of tubes 2 which are circumferentiallysurrounded by the second group of tubes 3 which are spaced radially fromthe first group of tubes 2 by the space 1. In this space 1 are situatedbaffles which form a baffle means for deflecting the partial gas streamsin the manner indicated by the arrows 15 and 16. Thus, an upper part ofthe gas stream at the tubes 2 is deflected axially to form a lower partof the gas stream at the tubes 3, while a lower part of the gas streamat the tubes 2 is deflected axially in an upward direction to form anupper part of the gas stream at the outer tubes 3. In this way it ispossible to achieve with a radial heat exchanger also the resultsdesired to provide a uniform temperature in the discharging gas stream.

Referring now to FIG. 13, there is shown therein in elevation a heatexchanger where the tubes are themselves curved so as to have theconfiguration of screws. Thus, this heat exchanger is also shown ashaving for the first group of tubes 2 the subgroups 11 and 12 and forthe second group of tubes 3 the subgroups 13 and 14. It will be seenthat the subgroups 11 and 12 are curved spirally in opposite directions,while the same is true of the subgroups 13 and 14, while the subgroups11 and 13 are twisted in the same direction and the subgroups 12 and 14are twisted in the same direction, so that the subgroups 11 and 14 aretwisted oppositely with respect to each other and the subgroups 12 and13 are twisted oppositely with respect to each other.

Therefore the portions of the entering stream 31 are directedcircumferentially respectively inopposite directions and are thendeflected further by baffles in the space 1 so that the outer stream atthe subgroup of tubes 12 forms the inner stream portion at the subgroup13 while the inner stream portion at the subgroup 11 forms the outerstream portion at the subgroup 14, as indicated by the arrows l5 and 16.In this way the stream portions or currents are deflected so as toreverse their relative positions. FIG. 13 shows how the entering innerheat exchanger fluid is supplied by way of a supply header 33, with thisinner heatexchanging fluid discharging through a discharge header 34.

The embodiment of FIG. 14 will also achieve the results of the inventionalthough it will be noted that in FIG. 14 the groups 2 and 3 are notsubdivided into subgroups and are twisted in the same direction. Thesetube groups communicate with each other in any suitable way while thespace 1 between the subgroups is provided with the baffles 10situated'between radial plates 4 in the manner described above and shownin H0. 5 or within cylindrical plates 4 as shown in FIG. 6. The severalhelically curved baffles which are thus distributed around the heatexchanger axis in the space 1 also deflect the entering stream after itflows beyond the tube group 2 so as to provide separate stream portionsflowing in the manner indicated schematically by the solid arrow anddotted arrow 16 to provide an interchange according to which the part ofthe entering stream adjacent the axis becomes the part adjacent theshell 17 at the second group of tubes 3 while the part of the enteringstream adjacent the shell 17 becomes the part adjacent the axis at thegroup of tubes 3.

Thus, with the above-described method and apparatus of the invention itbecomes possible to achieve a high degree of uniformity throughout theentire body of the discharging stream 32 without requiring complextubular arrangements and without creating any undesirable loss ofpressure.

What is claimed is:

1. In a heat exchanger, first and second groups of tubes communicatingwith each other for directing an inner heat-exchanging fluid along theinterior of said groups, said first and second groups of tubes having apredetermined relationship with respect to an axis of the heatexchanger, means for directing an outer heatexchanging fluid firstacross the exterior of said first group of tubes and then across theexterior of said second group of tubes to form from said outer fluid anentering stream distributed across said first group of tubes and anexiting stream distributed across said second group of tubes, saidentering stream being composed of first and second stream portions whichrespectively have first and second relationships with respect to saidaxis and second exiting stream also being composed of first and secondstream portions which have also said first and second relationships,respectively, with respect to said axis, and baffle means situatedbetween said groups of tubes for deflecting said first stream portion ofsaid entering stream to a location where said first stream portion ofsaid entering stream forms said second stream portion of said exitingstream and for deflecting said second stream portion of said enteringstream to a location where said second stream portion of said enteringstream forms said first stream portion of said exiting stream, so thatthe temperature of said exiting stream will be substantially uniform.

2. The combination of claim 1 and wherein said second group of tubescircumferentially surrounds said first group of tubes while said bafflemeans deflects said first and second portions of said entering stream inopposed directions, respectively, which extend substantially parallel tosaid axis.

3. The combination of claim 1 and wherein said first and second groupsof tubes are axially spaced from each other to occupy differentlocations along said axis, and said baffle means being situated in aspace between said first and second groups of tubes with said axisextending through the latter space, said baffle means deflecting saidfirst and second portions of said entering stream respectively inopposed directions which extend substantially radially with respect tosaid axis.

4. The combination of claim 3 and wherein said baffle means includes aplurality of baffle plates which divide said entering stream into aplurality of subsidiary streams each of which includes part of saidfirst portion and part of said second portion of said entering stream,said baffle means deflecting each part of said first portion and eachpart of said second portion of said entering stream throughapproximately before reaching said second group of tubes.

5. The combination of claim 3 and wherein said baffle means includes aplurality of cylinders through which said subsidiary streamsrespectively flow, said cylinders all having parallel axes which areparallel to said heat exchanger axis.

6. The combination of claim 3 and wherein said baffle means includesplates which define two groups of spaces which alternate with each otherand are distributed about said axis, and a plurality of connecting tubesextending through one of said groups of spaces for connecting saidgroups of tubes with each other so that they communicate with eachother.

7. The combination of claim 6 and wherein said baffle means includesdeflecting plates situated in the other group of spaces.

8. The combination of claim 3 and wherein said baffle means includebaffle plates of helical configuration defining channels through whichthe outer fluid flows while travelling from said first to said secondgroup of tubes.

9. The combination of claim 3 and wherein said first group of tubesincludes an inner section and an outer section surrounding said innersection, and said sections of said first group of tubes extendingspirally in respectively opposite directions for creating a whirling inthe entering stream.

10. The combination of claim 3 and wherein said baffle means includes aplurality of partition plates each situated in a plane containing saidaxis and said plates being uniformly distributed about said axis inplanes extending radially therefrom, and a plurality of deflectingplates situated between said partition plates.

11. The combination of claim 3 and wherein said means for directing theouter fluid across said groups of tubes includes an outer cylindricalwall within which said groups of tubes are located, and said bafflemeans extending up to said outer cylindrical wall with the latterparticipating in the control of the direction of flow of the outerfluid.

12. The combination of claim 1 and wherein said baffle means maintainsthe cross section through which the outer fluid flows from said first tosaid second group of tubes substantially unchanged so that deflectiontakes place without any substantial loss of pressure.

1. In a heat exchanger, first and second groups of tubes communicatingwith each other for directing an inner heatexchanging fluid along theinterior of said groups, said first and second groups of tubes having apredetermined relationship with respect to an axis of the heatexchanger, means for directing an outer heat-exchanging fluid firstacross the exterior of said first group of tubeS and then across theexterior of said second group of tubes to form from said outer fluid anentering stream distributed across said first group of tubes and anexiting stream distributed across said second group of tubes, saidentering stream being composed of first and second stream portions whichrespectively have first and second relationships with respect to saidaxis and second exiting stream also being composed of first and secondstream portions which have also said first and second relationships,respectively, with respect to said axis, and baffle means situatedbetween said groups of tubes for deflecting said first stream portion ofsaid entering stream to a location where said first stream portion ofsaid entering stream forms said second stream portion of said exitingstream and for deflecting said second stream portion of said enteringstream to a location where said second stream portion of said enteringstream forms said first stream portion of said exiting stream, so thatthe temperature of said exiting stream will be substantially uniform. 2.The combination of claim 1 and wherein said second group of tubescircumferentially surrounds said first group of tubes while said bafflemeans deflects said first and second portions of said entering stream inopposed directions, respectively, which extend substantially parallel tosaid axis.
 3. The combination of claim 1 and wherein said first andsecond groups of tubes are axially spaced from each other to occupydifferent locations along said axis, and said baffle means beingsituated in a space between said first and second groups of tubes withsaid axis extending through the latter space, said baffle meansdeflecting said first and second portions of said entering streamrespectively in opposed directions which extend substantially radiallywith respect to said axis.
 4. The combination of claim 3 and whereinsaid baffle means includes a plurality of baffle plates which dividesaid entering stream into a plurality of subsidiary streams each ofwhich includes part of said first portion and part of said secondportion of said entering stream, said baffle means deflecting each partof said first portion and each part of said second portion of saidentering stream through approximately 180* before reaching said secondgroup of tubes.
 5. The combination of claim 3 and wherein said bafflemeans includes a plurality of cylinders through which said subsidiarystreams respectively flow, said cylinders all having parallel axes whichare parallel to said heat exchanger axis.
 6. The combination of claim 3and wherein said baffle means includes plates which define two groups ofspaces which alternate with each other and are distributed about saidaxis, and a plurality of connecting tubes extending through one of saidgroups of spaces for connecting said groups of tubes with each other sothat they communicate with each other.
 7. The combination of claim 6 andwherein said baffle means includes deflecting plates situated in theother group of spaces.
 8. The combination of claim 3 and wherein saidbaffle means include baffle plates of helical configuration definingchannels through which the outer fluid flows while travelling from saidfirst to said second group of tubes.
 9. The combination of claim 3 andwherein said first group of tubes includes an inner section and an outersection surrounding said inner section, and said sections of said firstgroup of tubes extending spirally in respectively opposite directionsfor creating a whirling in the entering stream.
 10. The combination ofclaim 3 and wherein said baffle means includes a plurality of partitionplates each situated in a plane containing said axis and said platesbeing uniformly distributed about said axis in planes extending radiallytherefrom, and a plurality of deflecting plates situated between saidpartition plates.
 11. The combination of claim 3 and wherein said meansfor directing the outer fluid across said groups of tuBes includes anouter cylindrical wall within which said groups of tubes are located,and said baffle means extending up to said outer cylindrical wall withthe latter participating in the control of the direction of flow of theouter fluid.
 12. The combination of claim 1 and wherein said bafflemeans maintains the cross section through which the outer fluid flowsfrom said first to said second group of tubes substantially unchanged sothat deflection takes place without any substantial loss of pressure.